This invention is concerned with processes for the preparation of glycolaldehyde, and conversion thereof to ethylene glycol, by reaction of formaldehyde, carbon monoxide and hydrogen in the presence of a rhodium catalyst.
Ethylene glycol is a very valuable commercial chemical with a wide variety of uses including use as a coolant and anti-freeze, monomer for polyester production, solvent, and an intermediate for production of commercial chemicals.
Glycolaldehyde is a valuable intermediate in organic synthesis, including the preparation of serine, and is particularly useful as an intermediate in the production of ethylene glycol by catalytic hydrogenation.
The reaction of formaldehyde with carbon monoxide and hydrogen is a known reaction and yields, inter alia, ethylene glycol, methanol, and higher polyhydroxy compounds. For example, U.S. Pat. No. 2,451,333 describes the reaction of formaldehyde, carbon monoxide and hydrogen over a cobalt catalyst to produce mixtures of polyhydroxy compounds which include ethylene glycol, glycerol, and higher polyols. Various metal catalysts are also disclosed including nickel, manganese, iron, chromium, copper, platinum, molybdenum, palladium, zinc, cadmium, ruthenium and compounds thereof.
U.S. Pat. No. 3,920,753 describes the production of glycolaldehyde by reaction of formaldehyde with carbon monoxide and hydrogen in the presence of a cobalt catalyst under controlled reaction conditions, but with comparatively low yields.
Polyols are also produced by reaction of carbon monoxide and hydrogen over various metal catalysts. U.S. Pat. No. 3,833,634 describes this reaction catalyzed by rhodium to produce ethylene glycol, propylene glycol, glycerol, methanol, ethanol, methyl acetate, etc. Rhodium catalysts are also employed in the production of oxygenated derivatives of alkenes, alkadienes and alkenoic acid ester by reaction with carbon monoxide and hydrogen, as described, for example, in U.S. Pat. Nos. 3,081,357; 3,527,809; 3,544,635; 3,557,219; and 3,917,661.
The prior art processes for production of ethylene glycol have characteristically provided mixtures of products, the principal co-products being propylene glycol and glycerine, along with the lower alcohols, methyl and ethyl alcohol. Thus, these processes are encumbered by the need for expensive and time-consuming separation techniques where ethylene glycol is the desired product. In addition, the efficiency of the reaction in terms of yield of ethylene glycol is not high due to the concomitant formation of the co-products, which are usually present in significant amounts.
In accordance with U.S. Pat. No. 4,200,765 which is incorporated by reference herein, the reaction of formaldehyde, carbon monoxide and hydrogen over a rhodium-containing catalyst appears to involve a two-stage reaction, with the first stage yielding glycolaldehyde and methanol, and the second stage yielding ethylene glycol. Thus, this reaction is analogous to that realized with cobalt catalysts as collectively disclosed in the aforementioned U.S. Pat. Nos. 2,451,333 and 3,920,753, the surprising difference residing in the high selectivity of the process of U.S. Pat. No. 4,200,765 which exclusively leads to ethylene glycol as the sole detectable polyol obtained in the second stage of the reaction. Further, the conversion to glycolaldehyde realized in the first stage of the process of U.S. Pat. No. 4,200,765 is substantially greater than that obtained in the process described in U.S. Pat. No. 3,920,753.
When, in accordance with the preferred procedure, The process of U.S. Pat. No. 4,200,765 is carried out employing an aprotic amide solvent such as 1-methylpyrrolidin-2-one, 1-ethylpyrrolidin-2-one, 1-benzylpyrrolidin-2-one and N,N-diethylacetamide, the first stage conversion to glycolaldehyde proceeds very well with good yields and high formaldehyde conversion rates. However, in non-amide solvents, either of the protic or the preferred aprotic variety, yields of glycolaldehyde have been found to be comparatively poor.